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<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Berkeley DB Transactional Data Store Applications</dl></b></td>
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<p align=center><b>Why transactions?</b></p>
<p>Perhaps the first question to answer is "Why transactions?"  There are
a number of reasons to include transactional support in your applications.
The most common ones are the following:</p>
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<b>Recoverability</b><ul compact><li>Applications often need to ensure that no matter how the system or
application fails, previously saved data is available the next time the
application runs.  This is often called Durability.</ul>
<b>Atomicity</b><ul compact><li>Applications may need to make multiple changes to one or more databases,
but ensure that either all of the changes happen, or none of them
happens.  Transactions guarantee that a group of changes are atomic;
that is, if the application or system fails, either all of the changes
to the databases will appear when the application next runs, or none of
them.</ul>
<b>Isolation</b><ul compact><li>Applications may need to make changes in isolation, that is, ensure that
only a single thread of control is modifying a key/data pair at a time.
Transactions ensure each thread of control sees all records as if all
other transactions either completed before or after its transaction.</ul>
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